The present invention is directed, in general, to optical communications systems and, more specifically, to an optoelectronic device having an integrated capacitor formed thereon.
The bit-rate of optical fiber communications has increased significantly in recent years. However, transmission bit-rate has been restricted by the bandwidth of electrical circuits located in both the transmitter and receiver portions of optical telecommunications systems. As a means for increasing transmission capacity without being electrically restricted with respect to transmission speed, wavelength division multiplexing (WDM) transmission systems have been developed to overcome the dispersion of the optical fibers that limit the propagation length of high bit-rate signals.
In such systems, various manufacturers have proposed WDM systems using 40 or 80 wavelengths spaced by 100 or 50 GHz at 2.5 Gbit/sec. To simplify the wavelength management of such systems, wavelength tunable semiconductor lasers have become popular by offering the ability to increase the capacity, functionality and flexibility of such optical fiber networks. Potentially, such tunable lasers can simplify the architecture of such systems, as well as reduce their operating costs.
In addition, the importance of wavelength tunable lasers has been growing in fields other than WDM transmission systems, such as wavelength division switching systems, wavelength cross-connection systems, as well as in the field of optical measurement. No matter what the application, among the more popular choices for such tunable lasers are Distributive Bragg Reflector (DBR) semiconductor lasers. DBRs are made up of a multiplicity of transparent layers in which alternating layers of different indexes of refraction are formed typically by epitaxial growth and carriers can be injected through the DBR and into the optically active region. Wavelength tuning is accomplished with a tuning region within the DBR that uses a change in electrical current to finely tune the wavelength of the laser generated by the device.
Current optical fiber telecommunication systems are ideally suited for DBR lasers primarily because of their wavelength tunable characteristic. In fact, in such systems, it is well known that the use of DBR lasers results in a considerable increase both in transmission capacity and transmission speed. Unfortunately, problems with DBR lasers during operation commonly prevent such lasers from optimizing transmission within the optical networks. One particular problem is fluctuation in the current used by the tuning region of the laser to adjust the wavelength of the output. More specifically, current changes in other parts of a DBR laser, caused by the numerous radio frequency (RF) signals found throughout the device, typically lead to current leakage into the tuning region (commonly referred to as xe2x80x9ccross-talkxe2x80x9d). This current leakage often causes changes in the reflective spectrum of the grating located within the tuning region, which eventually changes the wavelength that is set by the tuning region. As a result, the laser generated by the DBR laser may have an undesirable wavelength. Furthermore, inductive pick-up by the device of RF signals in the device environment may lead to similar undesirable effects.
Perhaps the most common solution to the cross-talk problem is the use of a capacitor to filter the RF signals (and thus current leakage) traveling into the tuning region. Specifically, it has been discovered that a capacitor may be used to short-circuit these RF signals to ground, allowing the tuning region to control current flow within itself regardless of RF signal/current fluctuations occurring throughout the device. While the bonding of these discrete capacitor components with other electro-optic and optical components is possible, problems arise due to interaction of the specific attachment processes and wire bond length.
Accordingly, what is needed in the art is an optoelectronic device, for use with tunable lasers, that does not suffer from the deficiencies found in the prior art.
To address the above-discussed deficiencies of the prior art, the present invention provides an optoelectronic device. In one embodiment, the optoelectronic device includes a substrate having a first doped region adjacent a first outer surface and a second doped region adjacent a second outer surface. In addition, the optoelectronic device includes a wave guide located in the substrate and located between the first outer surface and the second outer surface. The optoelectronic device still further includes a capacitor located over one of the first outer surface or the second outer surface. The capacitor structure may be located on either one side or both sides as design may require.
In another aspect, the present invention provides a method of manufacturing an optoelectronic device. In one embodiment, the method includes forming a first doped region adjacent a first outer surface of a substrate, and forming a second doped region adjacent a second outer surface of the substrate. The method further includes creating a waveguide in the substrate, and forming a capacitor over one of the first outer surface or the second outer surface.
In yet another aspect, the present invention provides an integrated optoelectronic system. In one embodiment, the system includes at least one optical device having an optical substrate with a first doped region adjacent a first outer surface and a second doped region adjacent a second outer surface. At least one of the optoelectronic devices also includes a waveguide located in the substrate and located between the first outer surface and the second outer surface. In addition, this optoelectronic device includes a capacitor located over one of the first outer surface or the second outer surface. The integrated optoelectronic system further includes an optical fiber that is coupled to the optical device and is located on or within the semiconductor substrate. In addition, the system includes a detector coupled to the at least one optical device.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention.